It is known to use a laser beam to sever hair as an alternative to an arrangement of mechanical cutting blades. Hair exposed to a laser beam will absorb energy from that laser beam and the hair will either be severed by vaporisation or by laser induced optical breakdown and a resulting shockwave. A laser beam requires no moving parts and so the problem of cutting elements becoming worn or blunt is eliminated. Moreover, use of a laser beam to sever hair avoids skin irritation caused by the sharp edges of mechanical blades contacting the skin. It is known from WO1992/16,338 and U.S. Pat. No. 5,993,440 to provide a device including a laser diode and reflective elements that direct a laser beam across a cutting zone so that the beam is substantially parallel to and spaced from the surface of the user's skin during use. In this way, as the device is moved across the skin, hairs that enter the cutting zone are exposed to the laser beam and severed at the point of interaction between the laser beam and the hair.
Shaving performance is typically measured by two criteria—closeness of shave and irritation of the skin. The cutting height is the distance between the surface of the skin and the point at which hairs are cut. A good performing shaver should minimise the cutting height and therefore minimise the remaining hair length by cutting the hairs as close as possible to the skin. A good performing shaver should also minimise the variation in cutting height to attain substantially uniform remaining hair length. However, positioning a laser beam close to the skin may cause skin irritation if heat and energy from the laser is incident on the skin. It is necessary to protect the skin from a laser beam to avoid causing damage or irritation to the skin. In a different application, hair trimmers or groomers are used to trim hair to a constant length. In this case, although closeness may not be a major performance factor, uniformity of remaining hair length is desirable and minimising skin irritation remains an important consideration.
The skin surface of a user is not a flat and uniform environment. Skin, especially for example the face, typically has many contours, wrinkles and folds over which the shaver must be able to effectively move while maintaining a short and uniform cutting height. Moreover, it is known that when using a shaving device by pressing such a device against the skin, the skin will dome in the area of contact between the skin and the shaver and this can be further exaggerated when the device is moved across the skin.
Typically, to limit the effects of skin doming and protect the skin from the laser and limit irritation, a lamella is positioned between the laser beam and the skin to manipulate hair and limit contact between the skin and laser beam. A lamella is a generally planar member that is positioned between the cutting element (mechanical or optical) and the skin of a user during use, usually being in contact with the skin. A typical lamella has a plurality of apertures which allow hairs to protrude through and into the cutting area. However, use of a lamella on a shaving device can be detrimental to the closeness of cut as it increases the minimum attainable distance between the skin surface and the laser beam. Moreover, a lamella is typically provided with a plurality of apertures through which the hairs protrude as the lamella is moved over the skin. However, this arrangement means that not all hairs on the skin surface would be aligned with an aperture during a single pass and so not all hairs would be able to protrude through the lamella into the cutting zone, meaning that more passes over each area of skin are required. This is inconvenient and extra contact with the skin will increase rubbing and may increase the amount of skin irritation caused. Furthermore, use of a lamella can result in a build up of debris in the region of the laser beam, particularly hair off-cuts and dust generated by the cutting process. This debris can accumulate in the apertures of the lamella and in the vicinity of the laser beam and will reduce the hair-catching ability of the lamella and also the cutting efficiency of the laser beam.
It is known from WO2006/067721 to provide cutting heads of a mechanical shaver with flexible mounts such that as the mechanical cutting heads are moved across the surface of the skin their orientation changes in response to the contours and undulations of the skin surface. In particular, the cutting heads are sprung mounted about pivots so that they tilt backwards when pressure is applied to them and the springs act to push the cutting heads against the surface of the skin. In this way, as the shaver is moved over contours in the surface of the skin the cutting heads can move so that they are always flat against the skin surface and provide the most effective cutting action.
It is know from US2006/0200114 to provide a device for hair treatment that directs an optical beam in a direction towards a user's skin so that it severs hair on the user's skin. The device includes a lens that can alter the focal length of the optical beam and thereby alter the height at which hairs are severed. However, at least some of the energy of the optical beam will be absorbed by the user's skin and this may cause irritation or even injury.